designing rpd 321

8/3/2019 Designing RPD 321

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SDS321

McCrackens Removable Partial Prosthodontics.

Chapter 10 & 19


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Our objective should be the perpetual preservation of what remains

rather than the meticulous restoration of what is missing.


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Preserving what remains


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Designing RPD

On the basis of information gathered from the clinical examination

and the analysis of the study casts,


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Designing RPD

the components of an RPD framework are so

selectedthat the resulting design is estheticallypleasant and is least harmfulto the remaining tissues.


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As a result of the examination and diagnosis, thedesign of an RPD must originate on the diagnostic

castso that all the mouth preparation are carried outwith a specific design in mind. This could beinfluenced by the following factors,


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Factors influencing the RPD Design

1. One arch is to be restored or both

a. Orientation of the occlusal plane.

b. Space available for restoring missing teeth.


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c. Occlusal relationship of the remaining teeth.

d. Arch integrity and tooth morphology.

Overlay rest

Over-denture

Long rest

Over-denture

Vertical space

Retentive area


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2. Remaining abutment support / periodontal health / need for splintingor future additions.


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3. Tooth or Tooth & tissue supported prosthesis.


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4. Need for abutment modification clasp design.


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5. Type of major connector indicated e.g., a torus.6. Materials to be used for framework, bases, & teeth.


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7. Patients past experience, i.e., patients inability to accept

lingual bar or palatal bar major connector.


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8. Replacing a single tooth or anterior teeth RPD or FPD.


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Difference between two types of RPDs

Tooth Supported Tooth & tissue Supported

class III & IV class I & II

1. Support Abutment teeth Combination of abutment teeth

and soft tissues.


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class III & IV class I & II2. Impression Anatomic form Anatomic and functional forms

(altered cast technique).


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3. Indirect No denture rotation Needed to resist any denture base

Retention hence, not needed lifting away from the tissues.


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4. Base type Metal base no future Acrylic base future reline is

reline is required. anticipated due to bone loss.


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5. Clasp design Circlet/Embrasure/Ring Stress release design RPI /

No stress release RPC, - wrought wire clasp.


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Components of an RPD Framework

(Review)

Circumferential Clasps

Circlet / conventional / C clasp

Embrasure claspReverse action / Hairpin clasp

Ring clasp

Multiple clasp

Half & half clasp

Combination clasp


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(Review)

Infra Bulge or Bar type Clasps

1. T bar

2. Y bar

3. L bar

4. I bar


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system


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Factors for the Choice of a Direct Retainer

1. The type of an RPD:

a. tooth supported:- any type of clasp can be used.

b. tooth-tissue supported:- stress releasing (I bar) is used.

2. The location of the undercut on the abutment tooth in relation tothe saddle area (circlet / ring / hairpin).

3. The periodontal health of abutment (cast / wrought clasp).

4. The size of an abutment tooth (cast / wrought clasp).

5. The presence of a tissue undercut combination clasp.

6. Esthetic considerations I bar clasp in the distal undercut orcirclet clasp in the mesial undercut on anterior abutment.


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(Review)Maxillary Major Connectors

1. Single Palatal Bar

2. Single Palatal Strap3. U shaped Palatal Connector

4. Anterior & Posterior Palatal Straps / Bars

5. Palatal Plate


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Factors for the Choice of a Maxillary

Major ConnectorThe rigidity and location in relation to the gingivae and the

vibrating line posteriorly is critical.

1. Its design depends on the number and location of the saddleareas and emerges finally after connecting them together, e.g.,modified palatal strap or anterior posterior palatal straps majorconnectors.

2. Single palatal bar and U shaped connectors are seldom used.

The later design may be used in the presence of a large palataltorus.


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Components of an RPD Framework(Review)

Mandibular Major Connectors

1. Lingual Bar2. Lingual Plate

2b.Interrupted Lingual Plate

3. Double Lingual Bar

4. Labial Bar


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Factors for the Choice of a Mandibular

Major Connector

It must be rigid and properly located in relation to thegingivae and movable oral tissues.

1. Depth of anterior lingual sulcus (8 mm or less).

2. Periodontal health of the anterior teeth (bar or plate).

3. Class I edentulous arch may necessitate lingual plate

for additional resistance to horizontal rotation.

4. Anterior spacing (interrupted plate or Continuous bar).


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(Review)

Posterior Rest Seats

1. Occlusal rest.

2. Long occlusal rest.

3. Embrasure rest.

4. Onlay/overlay rest.


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(Review)

Anterior rest seats

1. Cingulum / inverted V rest.2. Ledge rest.

3. Ball rest.

4. Incisal rest.


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Selection of a Denture Base

Types:

1. Metal base (class III & IV).

2. Acrylic resin base (class I & II)

The single important factor in the design of a saddle area andfor the choice of a denture base material is the anticipated need forfuture reline.As class I & II RPDs may require future reline of thesaddle areas (to compensate for the bone loss due to the rotationalmovement occurring under occlusal load), an acrylic resin denture

base in indicated.


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Step by Step Procedure to Design

As a start, guiding planes should be marked on the proximalsurfaces of the abutment teeth adjacent to the saddle areas, accordingto the selected path of insertion.

Step 1: Plan Tooth Support

For bounded saddles, place the

prepared rest seats on the occlusal,

cingulum, or incisal surfaces of the

abutment teeth, near the edentulous

areas.

For distal extension saddleareas,the rest seats are placed on the mesial

side of the abutment, i.e., away from the saddle areas.


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Step 2: Design & Locate the Connectors.The final shape and form of the palatal major connector

develops after connecting the tooth supported and tooth-tissuesupported units of the arch together.

The choice of a mandibular major

connector, however, depends on thedepth of the anterior lingual sulcus.

The minor connectors will then be

placed to connect other parts of the

RPD (rests, retainers, artificial

teeth, etc..) to the major connector.


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Step 3: Plan Retention:Ideally, a direct retainer should be placed on either side of the

saddle area.Its location on the tooth is dependent on the presence ofa suitable undercut0.01.A bracing or

reciprocal arm should also be included.

For a distal extension saddle, an I-bar

retainer is preferred, as a part of RPI.

This design should also include an

indirect retainer to minimize rotation

of the denture base away from thetissues.


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Step 4: Connect retainers to the support units:Supra-bulge clasp is connected to the occlusal rest or the

guiding plate.Infra bulge clasp is connected to the mesh work minorconnector in the denture base.

Step 5: Outline and join the saddle areas(denture base)to these selected or

drawn components of the RPD

framework.


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Designing Mandibular Framework

Check List Locate Guide planes POI.

Plan Support.

Select the major connector.

Place the minor connectors forocclusal rests, clasps, artificial

teeth. Plan retention (direct & Indirect).

Connect the retainers to theframework components.

Outline and connect the saddleareas to the major connector.


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designing rpd 321

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